Pulmonary alveolus

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Diagram of the alveoli with both cross-section and external view

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Please Take Over This Page and Apply to be Editor-In-Chief for this topic: There can be one or more than one Editor-In-Chief. You may also apply to be an Associate Editor-In-Chief of one of the subtopics below. Please mail us [2] to indicate your interest in serving either as an Editor-In-Chief of the entire topic or as an Associate Editor-In-Chief for a subtopic. Please be sure to attach your CV and or biographical sketch.

An alveolus (plural: alveoli, from Latin alveolus, "little cavity"), is an anatomical structure that has the form of a hollow cavity. Mainly found in the lung, the pulmonary alveoli are spherical outcroppings of the respiratory bronchioles and are the primary sites of gas exchange with the blood. Alveoli are particular to mammalian lungs. Different structures are involved in gas exchange in other vertebrates.[1]


The alveoli are found in the respiratory zone of the lungs.


Alveolus diagram svg.png
Respiratory system complete svg.png

The lungs contain about 300 million alveoli[2]., representing a total surface area of approx. 70-90 square meters (m2). Each alveolus is wrapped in a fine mesh of capillaries.

The alveoli have radii of about 0.05 mm but increase to around 0.1 mm during inhalation.

The alveoli consist of an epithelial layer and extracellular matrix surrounded by capillaries. In some alveolar walls there are pores between alveoli.

There are three major alveolar cell types in the alveolar wall (pneumocytes):

  • Type I cells that form the structure of an alveolar wall
  • Type II cells that secrete surfactant to lower the surface tension of water and allows the membrane to separate thereby increasing the capability to exchange gases.
  • Macrophages that destroy foreign material, such as bacteria.

The alveoli have an innate tendency to collapse (atelectasis) because of their spherical shape, small size, and surface tension due to water vapor. Phospholipids, which are called surfactants, and pores help to equalize pressures and prevent collapse.


  • In asthma, the bronchioles, or the "bottle-necks" into the sac are restricted causing the amount of air flow into the lungs to be greatly reduced. It can be triggered by irritants in the air, photochemical smog for example, as well as substances that a person is allergic to.
  • Emphysema is another disease of the lungs, whereby the elastin in the walls of the alveoli is broken down by an imbalance between the production of neutrophil elastase (elevated by cigarette smoke) and alpha-1-antitrypsin (the activity varies due to genetics or reaction of a critical methionine residue with toxins including cigarette smoke). The resulting loss of elasticity in the lungs leads to prolonged times for exhalation, which occurs through passive recoil of the expanded lung. This leads to a smaller volume of gas exchanged per breath.
  • Chronic bronchitis occurs when an abundance of mucus is produced by the lungs. The production of this substance occurs naturally when the lung tissue is exposed to irritants. In chronic bronchitis, the air passages into the alveoli, the broncholiotes, become clogged with mucus. This causes increased coughing in order to remove the mucus, and is often a result of extended periods of exposure to cigarette smoke.
  • Cystic fibrosis is a genetic condition caused by the dysfunction of a transmembrane protein responsible for the transport of chloride ions. This causes huge amounts of mucus to clog the bronchiolites, similar to chronic bronchitis. The result is a persistent cough and reduced lung capacity.
  • Lung cancer is a common form of cancer causing the uncontrolled growth of cells in the lung tissue. Due to the sensitivity of lung tissue, such malignant growth is often hard to treat effectively.
  • Pneumonia is an infection of the alveoli, which can be caused by both viruses and bacteria. Toxins and fluids are released from the virus causing the effective surface area of the lungs to be greatly reduced. If this happens to such a degree that the patient cannot draw enough oxygen from his environment, then the victim may need supplemental oxygen.
  • Cavitary pneumonia is a process in which the alveoli are destroyed and produce a cavity. As the alveoli are destroyed, the surface area for gas exchange to occur becomes reduced. Further changes in blood flow can lead to decline in lung function.

Additional images


  1. Daniels, Christopher B. and Orgeig, Sandra (2003). "Pulmonary Surfactant: The Key to the Evolution of Air Breathing". News in Physiological Sciences. 18 (4): 151–157.
  2. http://www.maexamhelp.com/id109.htm

External links

Cost Effectiveness of Pulmonary alveolus

| group5 = Clinical Trials Involving Pulmonary alveolus | list5 = Ongoing Trials on Pulmonary alveolus at Clinical Trials.govTrial results on Pulmonary alveolusClinical Trials on Pulmonary alveolus at Google

| group6 = Guidelines / Policies / Government Resources (FDA/CDC) Regarding Pulmonary alveolus | list6 = US National Guidelines Clearinghouse on Pulmonary alveolusNICE Guidance on Pulmonary alveolusNHS PRODIGY GuidanceFDA on Pulmonary alveolusCDC on Pulmonary alveolus

| group7 = Textbook Information on Pulmonary alveolus | list7 = Books and Textbook Information on Pulmonary alveolus

| group8 = Pharmacology Resources on Pulmonary alveolus | list8 = AND (Dose)}} Dosing of Pulmonary alveolusAND (drug interactions)}} Drug interactions with Pulmonary alveolusAND (side effects)}} Side effects of Pulmonary alveolusAND (Allergy)}} Allergic reactions to Pulmonary alveolusAND (overdose)}} Overdose information on Pulmonary alveolusAND (carcinogenicity)}} Carcinogenicity information on Pulmonary alveolusAND (pregnancy)}} Pulmonary alveolus in pregnancyAND (pharmacokinetics)}} Pharmacokinetics of Pulmonary alveolus

| group9 = Genetics, Pharmacogenomics, and Proteinomics of Pulmonary alveolus | list9 = AND (pharmacogenomics)}} Genetics of Pulmonary alveolusAND (pharmacogenomics)}} Pharmacogenomics of Pulmonary alveolusAND (proteomics)}} Proteomics of Pulmonary alveolus

| group10 = Newstories on Pulmonary alveolus | list10 = Pulmonary alveolus in the newsBe alerted to news on Pulmonary alveolusNews trends on Pulmonary alveolus

| group11 = Commentary on Pulmonary alveolus | list11 = Blogs on Pulmonary alveolus

| group12 = Patient Resources on Pulmonary alveolus | list12 = Patient resources on Pulmonary alveolusDiscussion groups on Pulmonary alveolusPatient Handouts on Pulmonary alveolusDirections to Hospitals Treating Pulmonary alveolusRisk calculators and risk factors for Pulmonary alveolus

| group13 = Healthcare Provider Resources on Pulmonary alveolus | list13 = Symptoms of Pulmonary alveolusCauses & Risk Factors for Pulmonary alveolusDiagnostic studies for Pulmonary alveolusTreatment of Pulmonary alveolus

| group14 = Continuing Medical Education (CME) Programs on Pulmonary alveolus | list14 = CME Programs on Pulmonary alveolus

| group15 = International Resources on Pulmonary alveolus | list15 = Pulmonary alveolus en EspanolPulmonary alveolus en Francais

| group16 = Business Resources on Pulmonary alveolus | list16 = Pulmonary alveolus in the MarketplacePatents on Pulmonary alveolus

| group17 = Informatics Resources on Pulmonary alveolus | list17 = List of terms related to Pulmonary alveolus


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